While the present invention can be used in any system comprising a thumper assembly, it will be described herein for clarity as used in electrostatic marking systems such as monochrome or color xerographic developer systems.
In an electrostatographic reproducing apparatus commonly used today, a photoconductive insulating member may be charged to a negative potential, thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing powder referred to in the art as toner. During development, the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive insulating area. This image may be subsequently transferred or marked onto a support surface such as copy paper to which it may be permanently affixed by heating and/or by the application of pressure. Following transfer of the toner image or marking, the copy paper may be removed from the system by a user or may be automatically forwarded to a finishing station where the copies may be collected, compiled and stapled and formed into books, pamphlets or other sets.
Image consistency is important whether the copies are collected or compiled and formed into books, pamphlets, etc. One important property of print quality is the uniformity of the print. Many parameters of the xerographic process affect print uniformity, but one of the most important ones is consistency and quality of the developer used.
In one color system, an array or series of different color imaging stations are aligned above an endless belt. Each imaging station contains a raster output scanner (ROS), photoreceptor drum in a xerographic module, a development station and cleaning station. The ROS emits an electronic beam (laser) which impinges on the rotating photoconductive drum, thereby causing that location on the drum to undergo a change in electrical charge. As the drum continues to rotate past the development station, toner particles of a color which is unique to that imaging station will attach to the drum at the location charged by the ROS. This colored image is then transferred to an intermediate transfer belt that is passing by and in contact with the photoreceptor drum. As the intermediate belt passes by the different imaging stations (each containing a different color), it picks up subsequent color layers to create a complete color image which is then transferred to media.
Each colored beam must be in substantial registration with the other beams deposited on the belt for a proper final color copy. Also, each color station can be changed or varied when needed. In one embodiment, there are also two sensors (Mark On Belt or MOB sensors) that are fixed in position to a point on the machine frame such that the colored images pass within view of these sensors. These sensors serve to detect the quality of each color and can be used to indicate when a color change is required. This type of color system having an array of ROS units is generally described in U.S. Pat. No. 6,418,286 and is incorporated by reference into this disclosure.
As noted above, the consistency of the color image deposited on the drum is important to print quality. As the drum with the latent image continues to rotate, it passes through the development station which causes toner to stick to the drum where the electrical discharging (by the ROS) has taken place. The quality of the developed image is related to the consistency and quality of the developer material. Developer material is a mixture or blend of toner and carrier. The consistency or quality of the developer is a function of the consistency and quality of both the toner and the carrier. Toner is consumed regularly in the xerographic process and must be replaced at an equal rate. Toner replenishing systems exist to perform such a function. This constant replacement keeps the quality of the toner near the quality of new toner. Carrier is not consumed in the xerographic process and is subject to a constant churning in the developer unit. This constant churning causes the carrier to deteriorate over time. To counter this effect carrier can be added either with the toner or through a separate carrier replenishment system. The relationship of toner to carrier is a key parameter to the quality of the xerographic process. To maintain the relationship of toner to carrier, carrier must be removed or trickled out at the same rate it is added. This removal can be done through a trickle waste system which consists of transport system and a waste storage bottle. The waste bottle will eventually fill and will need to be removed and emptied or replaced.